Our long-term aim is to understand how sensory organs form. Sensory structures allow organisms to assess their environment, and sensory organ defects in humans lead to perceptive and psychological deficits. Lumen formation plays key roles in sensory organ development. Often, a tubular channel formed by glia or epithelia is penetrated by neuronal endings exposed to the environment to form the organ. How this coordinated tubulogenesis occurs is not known. Biological tubes allow liquid and gas flow in plants and animals. In humans, tubes are essential components of most organs. Defects in tube formation and maintenance, or ectopic formation of tubes, underlie numerous human disease states, including vascular aneurysms, intestinal herniations (diverticulosis), and congenital defects of the vasculature, intestine, kidney, and lungs. Excessive vascular tubulogenesis can support malignant growth. Little is known about the molecular mechanisms regulating tube lumen formation and size. The C. elegans amphid sensory organ is an excellent structure in which to study sense organ development. It is composed of 12 neurons with well-defined sensory roles, and two tube-forming glial cells that ensheath the neurons. Amphid architecture is remarkably similar to some sensory organ structures in Drosophila and mammals. Cells of the amphid are easily labeled with fluorescent reporter proteins, and their development can be examined in real time. Furthermore, genetics and molecular biology are generally facile in C. elegans, allowing for discovery of conserved molecular players regulating channel formation. We showed that a key regulator of C. elegans lumen formation is encoded by the daf-6 gene. DAF-6 protein is related to vertebrate and Drosophila Patched, and is expressed in all C. elegans tube classes, localizing to luminal surfaces. We have also shown that mutations in the wrt-6 hedgehog-like gene result in amphid defects similar to those of daf-6. The existence of a Hedgehog-Patched module has not been demonstrated in C. elegans and our results suggest that wrt-6 and daf-6 may indeed be such a module. Finally, we showed that LIT-1/Nlk kinase is a target of DAF-6 signaling, and is, thus, the first described target of Patched-related signaling in C. elegans. Here we propose three aims: (1) We will study the role of wrt-6 in lumen formation. (2) We will study lit-1 function in lumen formation. (3) We will clone previously isolated daf-6 suppressor mutations to reveal additional components of the new signaling pathway we discovered. Because Patched and related proteins are important in many aspects of human development and tumor formation, studies of the new signaling pathway we identified will help understand the functions of these key developmental proteins. In addition, our studies will provide insight into tubulogenesis, a process important for the formation of all organs, defective in congenital diseases, and hyperactivated in cancer. Public Health Relevance: Because Patched and related proteins are important in many aspects of human development and tumor formation, studies of the new signaling pathway we identified will help understand the functions of these key developmental proteins. In addition, our studies will provide insight into tubulogenesis, a process important for the formation of all organs, defective in congenital diseases, and hyperactivated in cancer.